Hitherto, in a motor control device, there is known a technology of detecting disconnection of a feedback loop line based on a current deviation between a current command and a measured value of a current flowing through a motor (hereinafter referred to as “current detection value”) when the feedback loop line for feeding back the current detection value is disconnected (for example, see Patent Literature 1).
As another conventional device, there is also known the following technology. Namely, when a power-supply voltage falls within an appropriate range, a motor rotation speed falls within a determination target range, an actual current value is equal to or smaller than a predetermined value, and a state in which an applied voltage or a voltage command is out of a predetermined corresponding range continues, it is determined that a power supply line to the motor is disconnected (for example, see Patent Literature 2).
In the case of the technology disclosed in Patent Literature 2, it is possible to detect the phase in which the disconnection has occurred by performing the above-mentioned determination processing for each of three phases in a motor including three-phase motor coils.
According to the above-mentioned method, a threshold value of the predetermined corresponding range of the voltage command is associated with a predetermined current value, which is a threshold value of the current, and a threshold value of the determination target range of the motor rotation speed. As a result, the determination based on a characteristic indicating an output limit of the motor, which is referred to as an N-T characteristic (rotation-speed-torque characteristic), is realized. Namely, the occurrence of disconnection is determined based on whether or not the value exceeds the output limit of the motor.